Expandable frame for silk screen



Jan. 25, 1966 P. J. DE GROOT 3,230,872

EXPANDABLE FRAME FOR SILK SCREEN Filed Sept. 24, 1963 2 Sheets-Sheet 1 FIG. .1.

INVENTOR. PHI LIP J. de GROOT ATTORNEYS Jan. 25, 1966 P. J. DE GROOT EXPANDABLE FRAME FOR SILK SCREEN 2 Sheets-Sheet 2 Filed Sept. 24, 1963 FIG. 4

FIG. 3

INVENTOR. PHILIP J. de GROOT ATTORNEYS United States Patent 01 3,230,872 Patented. Jan. 25, 1966 ice 3,230,872 EXPANDABLE FRAME FOR SILK SCREEN Philip J. de Groot, Cornwall Court, Oakland, Calif. Filed Sept. 24, 1963, Ser. No. 311,010 2 Claims. (Cl. 101-1271) This invention relates to an expandable or adjustable frame, especially a frame that may be used for stretching a silk screen of the type employed in silk screen printing.

The use of adjustable frames for mounting silk screens is, of course, well known to persons familiar with the art of silk screen printing. Conventional frames of this type usually comprise a pair of inner and outer frames, the innerframe comprising separately adjustable members disposed parallel to corresponding fixed members of the outer frame. A silk screen is secured to each of the adjustable inner frame members, and an adjustment of the inner frame members in the direction of respective parallel outer frame members will then produce a tensioning or stretching of the screen. Two or more screws or bolts are normally used to effect a movement of each inner frame members relative to its parallel outer frame member.

Although conventional frames, such as the kind described, are satisfactory for tightening the screen, they usually require careful adjustment of each of the inner frame members to insure that the corners are properly stretched. Moreover, since several screws or bolts must be operated to effect an adjustment of any one inner frame member, it is not easy to stretch a silk screenfrom each of four inner frame members with equal tension at all four corners. V

In brief, the present invention involves an expandable frame comprising a plurality of frame members having generally rectangular cross-sections held together in endto-end relationship by four corner guide brackets and the sheet of material (or silk screen) that is being stretched. Each corner bracket defines a pair of convergent U-shaped passages which receive the ends of two frame members, respectively, and having a movable abutment located at the intersection of its passages. Each abutment is threadably mounted on a screw member which, when turned, causes its abutment to be moved into engagement with the ends of the frame members, thereby causing them to be moved along the U-shaped passage within which it is received and extended relative to the corner bracket. Thus, the frame is expanded and the silk screen stretched between frame members by sequential operation of four screw members, which produces a corresponding movement of their abutments.

One principal object of this invention is, therefore, to provide an expandable frame comprised of frame members and improved corner brackets, each having a pair of U-shaped passages for receiving the ends of two frame members and a movable abutment for adjustably sliding those members relative to its passages.

Other objects are to provide: an expandable frame having few operating parts; a frame which may be manufactured at a reasonable cost; a frame that may be used to stretch a silk screen with uniform tension forces at each of its corners; and a frame which is easy to operate.

Additional objects of this invention will become apparent in view of the following detailed description and the accompanying drawings.

In the drawings forming a part of this application and in which like parts are identified by like reference numerals throughout the same,

FIG. 1 is a plan view illustrating a preferred embodiment of the invention in an expandable framework;

FIG. 2 is an enlarged detail of a portion of the framework shown in FIG. 1, illustrating one corner bracket and the complementary relationship of two frame members;

FIG. 3 is an enlarged section taken on lines 33 of FIG. 1; and I FIG. 4 is a diagrammatic illustration showing the manner in which the expandable frame is enlarged.

Referring to FIG. 1, framework 10 comprises four identical frame members 11, which are joined end-to-end by identical corner brackets 12 and held together by a piece of material 13 stretched between members. Frame members 11 possess a generally rectangular cross-section and are formed with a groove 14 fitted with a locking strip 15. Each locking strip is matable with its respective groove 14 together with one edge of sheet material 13, in a manner best shown in FIG. 3. It will be noted that the shapes of grooves 14 and locking strips 15 are such that a stretching of material 13 across framework 10 will not dislodge the strips from their respective groove. Furthermore, and with reference to FIG. 3, a stretching of material 13 tends to produce a clockwise rotation of strips 15 in the groove 14, thereby clamping the material with increased pressure in the area indicated by reference number 16.

The clamping action is a critical feature of the design shown. The cross section of groove 14 is designed with an interior dimension perpendicular to its length and parallel to the sheet material, in excess of the similar exterior dimension. With reference to FIG. 3, the interior dimension referred to is shown at 26. Dimension 26 is perpendicular to the length of groove 14 (the length is apparent when viewing FIGS. 1 and 2) and is parallel to the plane defined by the portion of sheet material 13 that is stretched between the frame members (see FIG. 1). Dimension 26 is greater than similar exterior dimension 27 shown in FIG. 4.

Locking strip 15 is provided, as shown in FIG. 3, with a cross section similar to the cross section of groove 14 and somewhat smaller. The cross-sectional dimension of strip 15 is less than the cross-sectional dimension of groove 14 so that locking strip 15 may be accommodated within groove 14- with the sheet material 13 in between (see FIG. 3). Thus the tolerance between locking strip 15 and groove 14 is approximately equal to the thickness of the sheet material 13.

Sheet material 13 is placed between locking strip 15 and groove 14 as shown in FIG. 3. Surface 28 of locking strip 15 is exposed, and sheet material 13 is stretched to the left (as viewed in FIG. 3), which tends to rotate locking strip 15 in a clockwise direction about it longitudinal axis.

Corner brackets 12 are made from metallic sheet material and shaped with a bottom portion 17 and perpendicular sides 18, 19, 20, 21 and 22. Sides 18 and 22, together with bottom portion 17, define a U-shaped passage which receives the end of one frame member 11. Similarly, upstanding sides 20 and 21 defines a U-shaped passage that receives the end of a second frame member 11. Sides 21 and 22 are interconnected and backed by a generally L-shaped bracket 23 having a flat corner portion 24; sides 18, 19 and 20 are connected, as by spot welding overlapping edges.

Retaining edges 25 and 26 which extend along and partially above respective U-shaped passages are provided integrally with the upper edge of sides 18 and 20, respectively, as shown in FIG. 3. Each edge engages the top surface and shoulder of the frame members, thereby confining said members within the U-shaped passages but allowing movement of the members along said passages.

In view of the above description, it will be evident that each corner bracket 12 slidably receives the ends of a pair each frame member 11 are heldwithin generally aligned passages of a pair of corner brackets 12 by sheet material 13, which are secured between members 11 on opposite sides of frame by locking strips 15.

Referring to FIG. 2, a movable abutment 27 is disposed at the intersection of each pair of convergent U- shaped passages. Abutments 27, which define angle plates, have a center portion 28 and a pair of side flanges 29 and 30, each side flange having a contact surface that extends in a plane perpendicular to the contact surface of the other flange. Each contact surface is also perpendicular to the axis of the frame member which it abuts. Center portion 28 is formed with a threaded opening that receives a screw member 31, said member being rotatably supported between side 19 and corner portion 24 of bracket 23. A hexagonal nut 32 is mounted to the exterior end of screw 31, and a washer member 33 is disposed between the nut and side 19. Screw 31, it will be seen, is mounted on an axis that extends transversely of both U-shaped passages. Therefore, as the screw is rotated abutment 27 will be caused to move along the screw, positioning the abutment either closer to or more distant from center portion 24. Moving abutment 27 in the direction of center portion 24 will, of course, move flanges 29 and against the ends of respective frame members 11, thereby causing said members to be moved along the U-shaped passages in which they are confined. A movement of abutments at all four corners brackets 12 will obviously produce a framework of enlarged peripheral dimension.

FIG. 4 of the drawings schematically shows the preferred manner of expanding a framework comprised of frame members numbered 1, 2, 3 and 4. The structural details of this framework are the same as previously described in connection with FIGS. 1-3. Beginning at one corner of the framework, such as corner bracket a, the bracket is operated to move its abutment in adirection toward members 1 and 2, causing them to occupy positions indicated by the broken lines la and 2a, respectively. Next corner bracket b is operated until its abutment produces an equal and opposite distortion of the frame such that members 3. and 4 assume the broken line positions of 3b and 4b. Brackets c and d are then operated in sequence to move members 2 and 4 into positions 2c and 4c, and frame members 1 and 3 into positions 1d and 3d. It is to be understood that the distortion of frame members shown in FIG. 4 is greatly exaggerated, and a tightening of any of the brackets does not require a reshaping of any of their U-shaped passages. Moreover, the best sequence of operation would entail multiple operation of each bracket in the sequential order described, thereby stretching material 13 at each of its corners in a progressive and increasing manner.

Although a preferred embodiment of this invention has 4 been shown and described, it is to be understood that various changesmay be made without departing from the spirit of the invention or the scope of the attached claims, and each of such changes is contemplated.

What I claim and desire to secure by Letters Patent is:

1. An expandable frame for stretching sheet material comprising: a plurality of frame members having generally rectangular cross sections held together in endto-end relationship by corner guide brackets; each of said frame members being formed with a groove on one side and extending lengthwise thereof, the cross section of said groove having an interior dimension perpendicular to the length thereof and parallel to said sheet material in excess of the similar exterior dimension thereof, said excess lying entirely on the side of said groove nearest the inside of said frame; a locking strip in said groove, said locking strip having a cross section similar to the cross section of said grove; said corner guide brackets having a bottom and upstanding sides that define a pair of convergent U-shaped passages which receive the ends of two frame members, respectively, in slidable relationship; said frame member being oriented such that said groove is located on the topside of said frame; a movable abutment disposed at the intersection of each pair of said convergent U-shaped passages, said abutment having a pair of contact surfaces for simultaneously engaging the ends of said frame members; and means for independently moving each of said abutments in a direction transverse to the U-shaped passages of its corner bracket, thereby adjusting the position of said abutment and sliad'bly moving said frame member along its associated U-shaped passage.

2. The expandable frame of claim 1 and sheet material stretched thercover, the edge portion thereof lying between said grove and said locking strip with one sur face with one surface of said locking strip exposed.

References Cited by the Examiner UNITED STATES PATENTS 1,711,670 5/1929 Brennan 101--128.1 X 1,916,022 6/1933 Schull 374.1 2,149,985 3/1939 Tepper 45130 2,588,199 3/1952 Bily 101-1271 2,925,774 2/ 1960 Scheeler l01127.1

FOREIGN PATENTS 1,080,684 6/1954 France.

122,640 7/ 1901 Germany.

ROBERT E. PULFREY, Primary Examiner.

DAVID KLEIN, Examiner.

HERMAN I. STRNISHA, EDGAR S. BURR,

Assistant Examiners. 

1. AN EXPANDABLE FRAME FOR STRETCHING SHEET MATERIAL COMPRISING: A PLURALITY OF FRAME MEMBERS HAVING GENERALLY RECTANGULAR CROSS SECTIONS HELD TOGETHER IN ENDTO-END RELATIONSHIP BY CORNER GUIDE BRACKETS; EACH OF SAID FRAME MEMBERS BEING FORMED WITH A GROOVE ON ONE SIDE AND EXTENDING LENGTHWISE THEREOF, THE CROSS SECTION OF SAID GROOVE HAVING AN INTERIOR DIMENSION PERPENDICULAR TO THE LENGTH THEREOF AND PARALLEL TO SAID SHEET MATERIAL IN EXCESS OF THE SIMILAR EXTERIOR DIMENSION THEREOF, SAID EXCESS LYING ENTIRELY ON THE SIDE OF SAID GROOVE NEAREST THE INSIDE OF SAID FRAME; A LOCKING STRIP IN SAID GROOVE, SAID LOCKING STRIP HAVING A CROSS SECTION SIMILAR TO THE CROSS SECTION OF SAID GROOVE; SAID CORNER GUIDE BRACKETS HAVING A BOTTOM AND UPSTANDING SIDES THAT DEFINE A PAIR OF CONVERGENT U-SHAPED PASSAGES WHICH RECEIVE THE ENDS OF TWO FRAME MEMBERS, RESPECTIVELY, IN SLIDABLE RELATIONSHIP; SAID FRAME MEMBER BEING ORIENTED SUCH THAT SAID GROOVE IS LOCATED ON THE TOPSIDE OF SAID FRAME; A MOVABLE ABUTMENT DISPOSED AT THE INTERSECTION OF EACH PAIR OF SAID CONVERGENT U-SHAPED PASSAGES, SAID ABUTMENT HAVING A PAIR OF CONTACT SURFACES FOR SIMULTANEOUSLY ENGAGING THE ENDS OF SAID FRAME MEMBERS; AND MEANS FOR INDEPENDENTLY MOVING EACH OF SAID ABUTMENTS IN A DIRECTION TRANSVERSE TOP THE U-SHAPED PASSAGES OF ITS CORNER BRACKET, THEREBY ADJUSTING THE POSITION OF SAID ABUTMENT AND SLIDABLY MOVING SAID FRAME MEMBER ALONG ITS ASSOCIATED U-SHAPED PASSAGE. 